Read Time 13 mins
Keywords
Sand Bubbler Crab
Sea shores
Microscopic life
Nitya is a filmmaker who shares a short mixed media animation film on the sand bubbler crab found on the shores of the Goan Coastline. Through her research and multimedia documentation, she discusses the criticality of this species and its place in our coastal ecosystem.
Sand bubbler crabs, true to their name, are found on sandy tropical and subtropical beaches of the Indo-Pacific region. They belong to the family dotillidae of the genus scopinera and dotillid. There are as many as 8 species of Dotilla and 15 species of Scopimera crabs. They have specialised air pockets on their legs and can soak up water through tiny hairs on their belly. The life of these crabs completely revolves around the tidal movement of the waves and since their activities are limited to low tide hours during the day, they work fast. They rest within their burrows during the high tide and feed on detritus and organic matter present in the sand during the low tide. With the help of their pincers; they scoop up moist sand, filter the essential components through their mouth parts and make sand balls with the remaining sand.
Sand Laddoo
3.05 mins
English
“ Why do they make sand balls? Why don't they just throw away the remaining sand on the beach? Why do they spend so much energy in making sand balls out of waste sand? The answer lies in the question itself. Sandballs = waste sand, meaning it's a visual cue for the crabs that all the nutritious food has been taken out of the sand.”
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If they want more food; they must go for the flat sand and not the sand balls. The sand balls are mostly spherical but are of different sizes depending on how big or small the crab is. The sandball size varies from 1 mm in diameter to 9mm. The crabs themselves are not larger than 1.5 centimetres and their body is spherical in shape. The colour of their body is just like the sand, providing them a very effective camouflage against predators. They have tiny eyes jutting out of their body, 4 pairs of limbs and a pair of pincers that are faced downwards to excavate sand. They work very fast in the intertidal area as they have to eat when the sand is moist. With just a normal activity of feeding, the sand bubbler crabs are in return filtering and purifying the sand and paying their contribution to the ecosystem.
One crab can only do a little but these crabs are an army of lakhs (1 lakh = 100000) and they single-handedly can make sand balls off a beach stretch of about a few kilometres. After they’ve had enough food and when the tide rises, they burrow a shallow hole in the sand, go into it and cover it completely from the inside leaving a tiny air bubble for them to live in. The waves go over the sand balls and disintegrate them into sand particles. The microscopic organic matter in the water is absorbed by the sand, bringing in a fresh new lot of sand for them to feed on. While new organic matter gets absorbed by the sand; the crabs rest within their burrows.
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“ They play a major role in keeping the coastal ecosystem clean by recycling the organic matter. Their absence would result in the accumulation of large amounts of organic matter in the sand eventually causing it to decay and stink.”
MR PARESH POROB
They play a major role in keeping the coastal ecosystem clean by recycling organic matter. Their absence would result in the accumulation of large amounts of organic matter in the sand eventually causing it to decay and stink. The life span of these crabs is around 5 years, provided they escape the eyesight of Sandpipers and other birds who eat them. So they also act as a source of food to other animals, keeping the food chain intact. Which means that the displacement of these small crabs would cause a large-scale disturbance in the food chain. With rising anthropogenic activities; there are higher chances of the habitat being unsuitable for the crab to live in. As a result of water sports and vehicular movement on the beach, sand compression takes place; making it unsuitable to be fed on. Oil, grease and harmful Microplastics in the water enter sand particles posing challenges to these tiny little sand bubbler crabs. Sand bubbler crabs play a critical role in the beach ecology by effectively cleaning sand and contributing to support the intricate food chains; hence it is important to prioritise the protection of their habitat to ensure the overall health and stability of coastal ecosystems.
Acknowledgements
Thanks to Padma Kamat and Paresh Porob
National Institute of Design, Madhya Pradesh
Riverbank Studios
